rebedding deck hardware

[mikestevens]

What is the absolute best compound for bedding deck hardware such as stanchions toerails, etc, onto fiberglass, cored decks?
Mike

[Ryan]

Mike

It is my experience that polysulfide is hard to beat for everything that is not plastic. Polysulfide will soften plastic, so it is no good for plexiglass ports, etc. But for everything else, it is great. Smells like hell, but seals great and stays flexible. If you use white, keep in mind that it will yellow with exposure to UV. You can get it in black and mahogany as well.

I am going on the assumption that all the holes that penetrate a cored area of the deck have been overdrilled and sealed with thickened epoxy. Is this the case? If not, that is a must to protect the core from water intrusion.

[osteoderm]

For most bedding, don't discount good old-fashioned oil-based bedding compound. Keep in mind that a good bedding compound is a sealant, not a glue, and only needs to be sticky enough to stay in place. Stay away from 3M 5200!
If you just have to have something modern and gluey, I'm liking BoatLife's Life Seal; a little easier to work with and far less aggressive than most straight polyurethanes. Where bedding is exposed to the elements (such as around the trim-plates of inboard chainplates), I'm having great results with 3M UV4000; far less aggressive than the other usual 3M suspects (less likely to tear chunks out of your gelcoat when pulling hardware), and far more resistant to the checking and chalking most modern goops exhibit in the sun.

[benz]

In my experience, and maybe I'm just bad at this, 3M 5200 is the only stuff that could keep water out of my boat. I did a good bit of business in Florida rebedding deck hardware whose bedding had leaked, in some cases catastrophically damaging boat interiors. Even when I pulled off hardware that had been bedded previously with 5200 (even that can leak if done poorly, of course), I never brought up chunks of gelcoat--I'm sure it happens from time to time, but 5200 is NOT guaranteed to ruin your gelcoat. I always rebedded with 5200, and none of my clients ever came back to complain of leaks.
I will say that if you're going to do it, do it right--slather the stuff everywhere, make sure it squishes out from under the fittings when you tighten them down, and then just wipe up the excess with paper towels and mineral spirits (note--do NOT use acetone! it will work, but not as well, nor as economically). If you bed your fittings properly, you may never have to unfasten them again, and gelcoat damage will not be a concern at all.
Happy gooping!
Ben

[osteoderm]

I too have been long-seduced by 5200, but am starting to move away from it for many bedding situations since I've found better products. I find it far better to regard 5200 as a glue rather than as a bedding. It's the best for pretty much permanent installs; through-hulls, extruded toe-rails, hull-to-deck joints etc.
With fittings subject to cyclical stresses from differing directions, some pad-eyes and definitely stanchion bases, the mechanical fastenings must be closely-fitted through properly-sized holes, any deck-core must be replaced by solid material in way of the fasteners, and substantial backing plates installed. I think that 5200 adheres strongly enough that it makes up for the wiggle in otherwise less-than-perfect installations.
Benz, I'm sure you've encountered this: a leaky stanchion base, poorly fit to the deck (maybe right over old non-skid?), fasteners through sloppy holes, stacks of fender washers below, and whatever old bedding all crumbled, dry, and poorly/inadequately applied. After cleaning off the old bedding surfaces and re-bedding with 5200 (plenty of squeeze-out, no air pockets), well yes, the leak is gone... but the essential underlying problems are not. I'm sure we can agree that no goop is a cure for inadequately-installed hardware.
If you've really gooped it down well, any removal will be a pain, and if the cleaning and application are at all wrong, the stresses and movement will eventually open a seam somewhere; 5200 is really only marginally flexible enough, especially once exposure has further hardened it, and relies entirely on adhesion to resist shearing forces.
Traditional "soft" beddings, either oil-based from a can, or basic 3M 101 in a tube, require a solid mechanical connection between pieces; they do nothing to hold things together or otherwise firm up a less-than-perfect situation. However, when things begin to creep and shift they work into seams, and there's no hard glue-line to break under shearing loads.
Then there's those "whoa-geez" situations when you just need to get something back together quick'n'dirty without a lot of prep hassles. Many sailors keep a tube or two of 5200 around just for that. In my locker, that's been replaced by a couple tubes of 3M UV4000 Fast Cure, but whatever works.

To address the original question: different applications, different goops; there is no single "absolute best compound". Ultimately, it's better to strive for perfect mechanical connections rather than rely on goop.

[benz]

Osteoderm is, of course, correct: any improperly installed hardware will give you grief regardless of bedding. And if you plan on removing a piece of hardware often, then a more temporary sort of bedding is in order anyway, since longevity isn't an issue. I got so sick of bedding and rebedding and worrying about leaks that I'm building a boat with a bulwark to bolt everything to: no bedding required. I even built special mountings into the fiberglass deck and cabintop so that less bolts would have to go through into the boat's inside; I've kept the number of holes from outside to in to a bare minimum, but I will be using 5200 on all of those--I don't expect ever to remove them again.
Best,
Ben